The present invention pertains to automotive steering wheels and more particularly, to a fiber-reinforced resin steering wheel. In a fiber-reinforced resin steering wheel a thermosetting resin, for example epoxy resin, is reinforced with a fiber material, for example glass or carbon fibers, and molded to a suitable shape or contour in a mold. The hub of the steering wheel is normally formed of metal which is placed in the mold and bonded to the fiber resin reinforcing material.
In a United Kingdom Pat. No. 2,063,145, there is disclosed a fiber resin reinforced steering wheel. The patent discloses a steering wheel whose rim and spoke portions are formed from a lightweight, hollow member or tube which is surrounded by a fiber-reinforced resin material. The steering wheel is fabricated by placing the flexible tube surrounded by the fiber-reinforcing which is preimpregnated with resin in a suitable mold. The mold is heated while supplying a high pressure gas to the inner flexible tube to expand the tube to press the surrounding fiber-reinforced resin against the mold cavity and allowing the thermosetting resin to set. The fiber reinforcing may comprise either carbon or glass fiber which is formed in the shape of a pipe or sock which is placed or threaded over the flexible tube.
While the above method provides a relatively lightweight strong steering wheel, it has the disadvantage of requiring fiber-reinforcing that is preimpregnated. The use of preimpregnated fiber reinforcing requires a special catalyst and high temperature cure. This results in a high cost and a slow cure of the resin, thus increasing manufacturing costs. Also, voids may result from the air which is trapped in the mold and compressed by expanding the flexible tube with high pressure gas. Even if steps are taken to vent the trapped air from the mold cavity some air will remain trapped in the resin and create voids. The presence of voids in the finished product can create stress areas and in extreme cases could cause failure of the part. Also, if the outer surface is to be used as a finished surface, any voids will detract from the appearance of the finished product. In the above patent, the problem of the appearance of the outer surface is solved by covering the outer surface with plastic, leather, wood or similar covering material. While the use of a covering provides a suitable appearance to the outer surface, it does add to the cost of the steering wheel. In addition to the molding problems the use of a one piece core structure requires some means for joining the spoke to the rim. This, of course, increases the cost of the core.